Head First Ajax covers: The JavaScript event model Making Ajax requests with XMLHTTPREQUEST objects The asynchronous application model The Document Object Model (DOM) Manipulating the DOM in JavaScript Controlling the browser with the Browser Object Model XHTML Forms POST Requests XML Syntax and the XML DOM tree XML Requests & Responses JSON -- an alternative to XML Ajax architecture & patterns The Prototype Library
The book also discusses the server-side implications of building Ajax applications, and uses a "black box" approach to server-side components.
Head First Ajax is the ideal guide for experienced web developers comfortable with scripting particularly those who have completed the exercises in Head First JavaScript and for experienced programmers in Java, PHP, and C# who want to learn client-side programming.